Three Degrees of Contagion

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The people we interact with influence us greatly - what we do, what we talk about and how we feel. However, science has found that our mood and behaviour is also influenced strongly by people we don't know. How is it that we are so strongly affected by people we've never met? And what can we do to maintain a healthier social network? This article by New Scientist magazine has the answers.

The following article ‘Three Degrees of Contagion’ was published in New Scientist magazine, edition 2689. It has been reproduced here for your information and enjoyment.

Three Degrees of Contagion

If you live in the northern hemisphere, this is probably not your favourite month. January tends to dispirit people more than any other. We all know why: foul weather, post-Christmas debt, the long wait before your next holiday, quarterly bills, dark evenings and dark mornings. At least, that is the way it seems. For while all these things might contribute to the way you feel, there is one crucial factor you probably have not accounted for: the state of mind of your friends and relatives. Recent research shows that our moods are far more strongly influenced by those around us than we tend to think. Not only that, we are also beholden to the moods of friends of friends, and of friends of friends of friends - people three degrees of separation away from us who we have never met, but whose disposition can pass through our social network like a virus.

Indeed, it is becoming clear that a whole range of phenomena are transmitted through networks of friends in ways that are not entirely understood:happiness and depression, obesity, drinking and smoking habits, ill-health, the inclination to turn out and vote in elections, a taste for certain music or food, a preference for online privacy, even the tendency to attempt or think about suicide.They ripple though networks “like pebbles thrown into a pond”, says Nicholas Christakis, a medical sociologist at Harvard Medical School in Boston, who has pioneered much of the new work.

At first sight, the idea that we can catch the moods, habits and state of health not only of those around us, but also those we do not even know seems alarming.It implies that rather than being in charge of where we are going in life, we are little more than backseat drivers, since most social influence operates at a subconscious level.

"We need not be alarmed. Social influence is mostly a good thing."

But we need not be alarmed, says Duncan Watts, a sociologist at Columbia University, New York.“Social influence is mostly a good thing.We should embrace the fact that we’re inherently social creatures and that much of who we are and what we do is determined by forces that are outside the little circle we draw around ourselves.”What’s more, by being aware of the effects of social contagion we may be able to find ways to counter it, or use it to our own benefit.“There’s no doubt people can have some control over their networks and that this in turn can affect their lives,” says Christakis.

To get an idea of what is going on, take Christakis’s findings on the spread of happiness, which were published last month.His team looked at a network of several thousand friends, relatives, neighbours and work colleagues who form part of the Framingham Heart Study, an ongoing multigenerational epidemiological survey they has tracked risk factors in cardiovascular disease among residents of Framingham, Massachusetts, since 1948.The found that happy people tend to be clustered together, not because they naturally orientate towards each other, but because of the way happiness spreads through social contact over time, regarding of people’s conscious choice of friends (BMJ, DOI: 10.1136/bmj.a2338).

Christakis also found that a person’s happiness is dependent not only on the happiness of an immediate friend but – to a lesser degree – on the happiness of their friend’s friend, and their friend’s friend’s friend.Furthermore, someone’s chances of being happy increase the better connected they are to happy people, and for that matter the better connected their friends and family.“Most people will not be surprised that people with more friends are happier, but what really matters is whether those friends are happy,” says Christakis.

Happiness is near

They also discovered that the effect is not the same with everyone you know.How susceptible you are to someone else’s happiness depends on the nature of your relationship with them. For example, if a good friend who lives within a couple of kilometres of you suddenly becomes happy, that increases the chances of you becoming happy by more than 60 per cent.In contrast, for a next-door neighbor the figure drops to about half that, and for a nearby sibling about half again.Surprisingly, a cohabiting partner makes a difference of less than 10 per cent, which coincides with another peculiar observation about some social epidemics:that they spread far more effectively via friends of the same gender.

All this poses a key question:how can something like happiness be contagious?Some researchers think one of the most likely mechanisms is empathetic mimicry.Psychologists have shown that people unconsciously copy the facial expressions, manner of speech, posture, body language and other behaviours of those around them, often with remarkable speed and accuracy. This then causes them, through a kind of neural feedback, to actually experience the emotions associated with the particular behavior they are mimicking.

Barbara Wild and her colleagues at the University of Tubingen, Germany, have found that the stronger the facial expression, the stronger the emotion experienced by the person observing it (Psychiatry Research, vol 102, p 109).She believes this process is hard-wired, since it acts so rapidly and automatically.

Others have suggested it works through the action of mirror neurons, a type of brain cell thought to fire both when we perform an action and when we watch someone else doing it, though it is not clear whether the mimicking would cause the neurons to fire or whether their firing would trigger the mimicry.What is clear is that unconscious imitation allows people to “feel a pale reflection of their companions’ actual emotions” and even “feel themselves into the emotional lives of others”, says Elaine Hatfield at the university of Hawaii, Honolulu, whose review of the latest research will appear next April in The Social Neuroscience of Empathy.

"There is plenty of evidence for emotional contagion."

There is plenty of evidence for emotional contagion outside the lab.In 2000, Peter Totterdell at the University of Sheffield, UK, found a significant association between the happiness of professional cricketers during a match and the average happiness of their teammates, regardless of other factors such as whether the match was going in the teams’ favour (Journal of Applied Psychology, vol 85, p848).He found a similar effect among nurses and office workers.It has also been shown that if a college student suffers from mild depression their roommate will become progressively more depressed the longer they live with them and that emotional displays by bank employees have a direct impact on the moods of their customers.

We can see, then, how a phenomenon such as happiness might pass quickly though a social network and infect clusters of friends and relatives.What none of these studies explains, however, is why the strength of the infection varies according to who is passing it to whom.Why are we so much more strongly affected by the happiness of a nearby friend than a nearby sibling?Why does a next-door neighbour have a significant impact, yet someone living a few tens of metres away on the same block have none?

The power of strangers

Two factors appear crucial:the frequency of social contact, and the strength of the relationship.This is not too surprising: we know that emotional contagion requires physical proximity.It is also likely that the closer we feel to someone, the more empathetic we are towards them, and the more likely we are to catch their emotional state.However, how these two factors play out in day-to-day interaction is uncertain.What is also unclear – because it has never been properly tested – is the extent to which emotions can propagate through virtual networks, where the opportunity for physiological mimicry is much reduced.

So much for emotions – what about other phenomena that we unwittingly pick up, and pass on through our social networks?In 2007, Christakis’s team, again tracking members of the Framingham Heart Study, found that obesity is transmitted in a similar way to happiness.Your risk of gaining weight increases significantly when your friends gain weight, and it is also affected by the weight of people beyond your social horizon.“Obesity appears to spread through social ties,” Christakis says.Again, how likely you are to catch it depends on who you are interacting with: after controlling for factors such as difference in socioeconomic status, the researchers found that an individual’s chances of becoming obese increased by 57 per cent if one of their friends became obese, 40 per cent if a sibling did and 37 per cent if their spouse did, irrespective of age (The New England Journal of Medicine, vol 357, p370).

"Obesity spread via a different mechanism to happiness."

However, neighbours have no influence, and how far away you live from a friend counts for little, which implies that obesity spreads via a different mechanism to happiness.Rather than behavioural mimicry, the key appears to be the adoption of social norms.In other words, as I see my friends gain weight, this changes my idea of what an acceptable weight is.One similarity with happiness is that friends and relatives have a far greater influence if they are of the same gender.While it is not evident why that should matter for emotional contagion, norms of body size are clearly gender-specific:“Women look at other women, men look at other men,” says Christakis.This could also help explain the epidemics of eating disorders reported among groups of schoolgirls in recent decades.

The spread of a social norm appears to account for another of Christakis’s findings:that when people stop smoking, the usually do so along with whole clusters of friends, relatives and social contacts.As more people quit, it becomes the socially acceptable thing to do, and those who choose to continue smoking are pushed to the periphery of the network.In this case, people are most strongly influenced by those closest to them – if your spouse quits, it is 67 per cent more likely that you will too.Your work colleagues can also have an effect, particularly if you are in a small, close-knit workplace; and more highly educated friends influence one another more than less educated (The New England Journal of Medicine, vol 358, p 2249).

Happiness, obesity, smoking habits – activities that we traditionally think of as shaped by individual circumstances, turn out to be ruled to a large degree by social forces.Many other day-to-day phenomena fit a similar pattern, often counter-intuitively.Take autism: Peter Bearman at the Institute for Social and Economic Research and Policy at Columbia University who in 2004 uncovered a link between suicidal behavior and certain friendship patterns (American Journal of Public Health, vol 94, p 89), is looking at whether the recent rise in the diagnosis in autism is in any way socially determined.His study is ongoing, but he says his findings could be “explosive”.“It is likely that if you have an autistic child in your community the probability of your child being diagnosed with autism is significantly higher.”

Why three degrees?

While the mechanism of social contagion varies depending on the phenomenon being spread, in many cases the dynamics are very similar.For example, Christakis has found that with happiness, obesity and smoking habits, the effect of other people’s behaviour carries to three degrees of separation and no further.He speculates that this could be the case with most or perhaps all transmissible traits.Why three degrees?One theory is that friendship networks are inherently unstable because peripheral friends tend to drop away.“While your friends are likely to be the same a year from now, your friends of friends of friends of friends are likely to be entirely different people,” says Christakis.

This poses the question:what shapes the architecture of our social networks and our position in them?Clearly, may factors contribute:where we live, where we work, family size, education, religion, income, our interests, and our tendency to gravitate towards people similar to us.New research by Christakis’s team, due to be published in the next few weeks, suggests there is also a strong genetic component.The study compared the social networks of identical and fraternal twins, and found that identical twins had significantly more similar social networks than fraternal twins, suggesting the structure of your social network is influenced by your genes.That may not sound remarkable, since personality traits such as gregariousness and shyness clearly play a role in determining how connected we are.But there is much to it, says Christakis.“It’s not just about having a genetic predilection to be friends with a lot of people, it’s about have a genetic predilection to be friends with a lot of popular people.That’s mysterious:how could our genes determine our actual location in this sociotopological space?”

Answering that should help us understand more about the “collective intelligence of social networks, which some researchers liken to the flocking of birds – the decisions to quit smoking, for example, is no more an isolated move that the decision by a bird in the flock to fly to the left.Sociologists and others are using mathematical models to test these dynamics to try to understand better what triggers the spread of behaviours.Duncan Watts at Columbia University has shown that adding localised social groups with certain ideas or behaviours can lead to the ideas cascading across entire global networks.This contradicts the notion – promoted by the author Malcolm Gladwell in The Tipping Point and others – that social epidemics depend on a few key influential individuals for whom everyone else takes their cue.It doesn’t ring true, argues Watts, because such “influentials” typically interact with only a few people.The key for the spread of anything, he says, from happiness to the preference for a particular song, is a critical mass of interconnected individuals who influence one another.

"Is there any way to mitigate the effects of these social forces?"

Is there any way to mitigate the effects of such powerful and pervasive social forces? It is unlikely we can ever escape social influence entirely, even if we wanted to.“Even when you’re aware of it, you’re probably still susceptible,” says Watts.Still, being aware can help, especially when we are seeking to avoid undesirable behaviours or adopt positive habits.We can be choosy about new friends, seeking out people whose lifestyles we aspire to:if you want to lose weight, for example, join a running club and – most importantly – socialise with its members.

Actually cutting ties with old friends might be a bit drastic, though perhaps spending less time with those whose traits we do not wish to share would be a good idea – lazy people, perhaps, or those inclined to negative thinking.And beware those who hang out with such people even if they do not display their views or behaviours – remember the three degrees of contagion rule.Finally, if you really cannot avoid spending time with certain people whose behaviours or emotional state you would rather not take on board (certain relatives at family gatherings, perhaps), you could always try repressing your natural inclination to mimic their body language and facial expressions, and so limit the contagion effect – though be prepared for them to instinctively cool towards you as a result.

What this game plan amounts to is a kind of subtle social reorientation.We will always be vulnerable to what those around us are doing, so as far as possible make sure you are with the right people.Remember the new adage: we are who we hang out with.

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Five tips for a healthier social network

1.Choose your friends carefully.2.Choose which of your existing friends you spend the most time with.For example, hang out with people who are upbeat, or avoid couch potatoes.3.Join a club whose members you would like to emulate (running, healthy cooking), and socialise with them.4.If you are with people whose emotional state or behaviours you could do without, try to avoid the natural inclination to mimic their facial expressions and postures.5.Be aware at all times of your susceptibility to social influence – and remember that being a social animal is mostly a good thing.